Eye, Brain, and World
Rice University Alumni College
March 2, 2003, Jones School Auditorium

James R. Pomerantz (pomeran@rice.edu), 713-348-3419, Sewall Hall 492A

Focusing slide: Perception Puzzle

Ten Introductory Questions

1.     Why is it that a pencil appears to bend when it is stuck into a glass of water?
2.     Why does the world look right side up when the lens of the eye makes the retinal image upside down?
3.     Why does the moon look bigger when it is low in the sky, near the horizon, than when it is high in the sky, near the zenith?
4.     How is it that we can tell that two lines do not line up (i.e., are not collinear) when they are ‘off’ collinearity by a distance that is less than half the diameter of a rod or cone?
5.     When does the apparent pitch of a siren change as an ambulance or fire engine passes you?
6.     Why are so few textbooks or newspapers printed with yellow ink on white paper?
7.     Given that our senses sometimes play tricks on us, how can we be sure that the ‘real world’ out there really exists?
8.     How could you tell whether dogs can see colors?  Whether human infants can see colors?
9.     Why do the stripes on a barber pole appear to move up when we know intellectually that the pole is just spinning horizontally?  More generally, when does our intellectual knowledge of the world affect what we perceive?
10. What would it take to construct a robot that could recognize dogs and tell them from cats, etc.?  (Cf. bar code scanners).

Vision is the best understood and perhaps the most important perceptual system for humans

Perception is an important area of inquiry because:

Perception is the key mediator between stimulus and response
Perception is the source of most knowledge that humans acquire.

Perception is interdisciplinary, embracing art (including music), philosophy (epistemology, logic), mathematics, engineering, biology, medicine, psychology, and other fields.

Perception is largely an unconscious process, and thus it complexity tends to be underestimated

Perception is transparent to the perceiver – we notice it only when it misfires.  Examples: the blind spot; neglect.

Researchers failed to appreciate the magnitude of the problem of perception until we tried to simulate the process (Marvin Minsky, MIT, artificial intelligence).

Perception can seem impossible (as with the flight of bumblebees), but fortunately, the stimulus field is redundant, resulting in  over-determination.

Our subjective notions of how perception works are naïve.  Example: Superman’s x-ray vision.

The key function of perception, including all its components is survival.  The key information source comes from the constancies, invariants that tell you about the world.

Perception involves a complex chains of events.  There exist multiple links in vision, audition.

Eight facts about perception.  Perception:  

  1. Is limited: Infrared Scene, Dust Mite, Edgerton Bullet, Powers of Ten

  2. Is selective

  3. Requires memory

  4. Is not entirely veridical (trustworthy): Hermann Grid, Spiral Illusion, Simultaneous Contrast

  5. Takes time: Metacontrast, Slow Metacontrast

  6. Corresponds more to the distal than to the proximal stimulus: Shepard Boxtops, Adelson Shadow Effect, Lightness Constancy

  7. Involves the active organization of sensory information: Hexagram of Spot Circles, R. C. James Photograph, Necker Cube, Subjective Necker Cube   (Bradley, Dumais, and Petry, 1976)

  8. Focuses on change, not on steady-state information.

Study a black-box system by:

  1. Peeking inside (PET scans, fMRI)

  2. Measuring the system's response time (human RT studies)

  3. Looking for errors the system makes (illusions)

Illusions (for more, see:

Illusionworks  Note: the original site is down so click here for archived site.
www.michaelbach.de/ot/index.html

  1. Optical - ones that originate in the world, not in us (grass is greener; pencil in water)

  2. Perceptual - early (e.g., floaters, afterimages, rubber pencil; aftereffects - short and long term)

  3. Perceptual - late (Muller-Lyer, rainbow, metamers in color, barberpole motion)

Illusions in the 'real world': seven moon illusions

  1. Size at horizon

  2. Moon through moving clouds

  3. Moon through side car window

  4. Moon completion

  5. Man in the moon

  6. Craters  depth illusion

  7. Disk (vs. globe) illusion

 

Good, recent books on vision:

Vision and Art: The Biology of Seeing, by Margaret Livingstone.  Harry N. Abrams, Inc, 2002.
Visual Science: From Photons to Phenomenology, by Stephen E. Palmer.  MIT Press, 1999.
Eye & Brain, by Richard L. Gregory.  Princeton University Press, 1997.
The Cognitive Neuroscience of Vision, by Martha Farah.  Blackwell, 2000.
 Sensation & Perception (5th edition), by E. Bruce Goldstein. Brooks/Cole, 1999
 Visual Perception: Essential Readings, Steven Yantis, Editor. Psychology Press, 2000.

 

Reference on McCollough effect (red and green vertical and horizontal stripes) which I probably will not be able to demonstrate for you:
McCollough, Celeste (1965). Color adaptation of edge-detectors in the human visual system. Science, 149, 9 1115­1116.

 

Minsky - Papert spirals

Brain MRI (left saggital view)

Visual Cortex

Brain Pathways

Retina Layers

Stroop Effect

Motion aftereffect with rotating spirals: see www.discover.com/dec_99/brainworks.html